The present invention relates generally to a road map display system for displaying a road map and symbols representing the positions of a vehicle and a designated destination on a screen. More particularly, the invention relates to a road map display system which displays the relationship between the vehicle position and destination and updates the display according to the movement of the vehicle.
A display system for displaying the road map and the vehicle position on the display road can help the vehicle driver find his way. A pilot system for a ship is disclosed in the first publication of the Japanese Patent Application Sho 52-159895 (Tokkai Sho 54-89767, published July 17, 1979). In this publication, there is shown a method for displaying a sea chart with an indication of the ship position. The sea chart is moved on the display according to the travelling distance and travelling direction of the ship. In this system, coordinates of the displayed sea chart are modified with respect to the position and travelling direction of the ship. The sea chart is stored in a digital memory as plotted coordinates. A microcomputer is used for processing modifications of the sea chart coordinates and for calculation of the ship position based on a sensor, which measures travelling distance and detects the direction of the ship.
On the other hand, in the automotive vehicle field, Tokkai Sho 52-141662, published on Nov. 26, 1977, shows a map display system for an automotive vehicle. In this system, microfilm is used to store the map. In this system, the indication of the vehicle position will move in accordance with the travelling distance and travelling direction of the vehicle.
In such road map display systems for automotive vehicles, it is convenient to display symbols for both the vehicle and the destination on the displayed map. It would be even more convenient to display the relationship between the vehicle and the destination by displaying the map on a coordinate system centered between the vehicle position and the destination. Also, the displayed map would be most easily legible if the y-axis of the display coordinate system were always parallel to the travelling direction of the vehicle.